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Jquery/Ajax to get database using php

I have an HTML page that is too big to post on here, however I'll just post the ajax/jquery I am using to try and access the PHP file variables.
threadPage.html
<script type="text/javascript">
$.ajax({
url : '/ThreadCreation.php',
type : 'POST',
data: {'titles': titles}
crossDomain: true,
dataType : 'jsonp',
success : function (data) {
console.log(data) /
},
error : function () {
alert("error");
}
})
</script>
<!-- bunch of html -->
So essentially I am trying to get the variable from the ThreadCreation.php in JSON form. It should be in an array so that I can loop through it in the HTML file.
ThreadCreation.php
<?php
$username = 'root';
$password = '';
$db = 'main_database';
$conn = mysqli_connect('localhost', $username , $password,$db);
if (!$conn){
die("unable to connect");
}
$sql = mysqli_query($conn, "SELECT title FROM thread");
while($row = mysqli_fetch_array($sql)) {
$titles[] = $row['title'];
echo json_encode($titles);
?>
I will repeat though, that this HTML file is only getting information from the database through PHP. So there is no form submission here.
I keep getting that 'titles is not defined'. This makes sense because there is not titles defined in the HTML, however I am unsure how to construct my ajax request to collect the data, as this format is all I have seen people use.

Mention empty array first just to prevent error in case you have no data
in database then empty array will proceed.
$sql = mysqli_query($conn, "SELECT title FROM thread");
$titles = array();
while ($row = mysqli_fetch_array($sql)) {
array_push($titles,$row['title']); // Push data in empty array
}
echo json_encode($titles);

How to get an value from a php page with js

I am trying to capture a value that is calculated on a PHP page called "classes_day.php" at the same time as I pass a value per GET, "? Day = YYYY-mm-dd" to it. How do I do this with JS or JQuery?
<?php
// aulas_dia.php
include '../config.php';
$exped_duration = 14*60;
if (isset($_GET['data'])) {
$data = $_GET['data'];
$query = "SELECT * FROM `task` WHERE `dia` LIKE ".$data."";
$result = mysqli_query($link,$query);
$soma = 0;
while ($row = mysqli_fetch_assoc($result)) {
$soma = $soma+$row['duration'];
}
$aulas_free = floor(($exped_duration-$soma)/50);
echo $aulas_free;
}
?>
I already tried using an iframe and contentwindow, but iframe gets the value and the contentwindow is empty (weird isn't it?).
Following Barmar's tip, I'm using $ .get, but I don't know why this loop is not working, can anyone help me?
for (i = 0; i < num_days; i++) {
x = (first_day+i)%7;
y = (first_day+i-x)/7;
h_dia(String(y)+String(x),i+1);
data_c = ano+"-"+mes+"-"+String(i+1);
$.get("aulas_dia.php?data="+data_c, function(data){
console.log(String(y)+String(x)+" - "+data_c+" - "+data);
set_aulas_fun(String(y)+String(x),data);
});
}

Use $.get() to send an AJAX request.
$.get("classes_day.php?data=YYYY-MM-DD", function(response) {
console.log(response);
});
BTW, you can add up all the durations in the SQL query instead of using a PHP loop. And you should use a prepared statement to prevent SQL injection.
<?php
include '../config.php';
$exped_duration = 14*60;
if (isset($_GET['data'])) {
$data = $_GET['data'];
$query = "SELECT SUM(duration) AS total FROM `task` WHERE `dia` LIKE ?";
$stmt = $link->prepare($query);
$stmt->bind_param("s", $data);
$stmt->execute();
$result = $stmt->get_result();
$row = $result->fetch_assoc();
$soma = $row['total'];
$aulas_free = floor(($exped_duration-$soma)/50);
echo $aulas_free;
}

Javascript inside PHP MYSQL query

I know that using php inside js is a bad practice, but unfortunately for now my skill is not enough to come up with something else.
$(document).ready(function() {
$("#type").change(function() {
var val = $(this).val();
valSize = "<?php $sql = "SELECT model FROM cars WHERE brand = 'val'";
$result = mysqli_query($conn, $sql);
while($row = mysqli_fetch_assoc($result)){
echo '<option>'.$row['model'].'</option>';
}
?>";
$("#size").html(valSize);
});
});
Is there any way how I could add val variable inside php code?

Your best bet would be to use a JavaScript AJAX call to send a request to another php file on your server.
First, create a separate PHP file on your server, I'll label it query.php (ONLY for the purposes of this explanation, I'd recommend choosing something more meaningful to your application).
<?php
if ($_POST['brand']) {
// Be sure to set up your SQL $conn variable here
$conn = ...;
$sql = "SELECT model FROM cars WHERE brand = '" . $_POST['brand'] . "'";
$result = mysqli_query($conn, $sql);
$data = []; // Save the data into an arbitrary array.
while ($row = mysqli_fetch_assoc($result)) {
$data[] = $row;
}
echo json_encode($data); // This will encode the data into a variable that JavaScript can decode.
}
Then in your JavaScript, perform the AJAX request:
$(document).ready(function() {
$("#type").change(function() {
var val = $(this).val();
$.post('query.php', {'brand' : val}, function(data){
var jsonData = JSON.parse(data); // turn the data string into JSON
var newHtml = ""; // Initialize the var outside of the .each function
$.each(jsonData, function(item) {
newHtml += "<option>" + item['model'] + "</option>";
})
$("#size").html(newHtml);
});
});
});

You can't execute the php code once the page has loaded. You're going to have to make a ajax call to a php file, that queries the data you need and echos that back to the original file. I would also recommend encoding it using echo json_encode($queryResults); Then you can JSON.parse($data);the return data in the success function of the ajax call.

JQuery GET request won't get correct data from php echo

I am trying to fill a table using a jquery .get request, the url being a php file. The php gets data from a database, then it should return a json array back to the jquery, array which will fill the table. While the length of the array is returned as it should, the table cells are empty.
Here is my get.php function:
<?php
$mysqli=new mysqli("localhost:3306","root","","leagues");
if (mysqli_connect_errno())
{
printf("Connect failed: %s\n", mysqli_connect_error());
exit();
}
$return_arr = array();
$query = "SELECT * FROM league";
if ($result = $mysqli->query($query)) {
while ($row = $result->fetch_row())
{
$return_arr[] = $row;
}
}
$mysqli->close();
header('Content-Type: application/json');
echo json_encode($return_arr);
?>
And here is my jquery get function
$.get('php/get.php',function(responseJson)
{
if(responseJson!=null)
{
$("#tableleague").find("tr:gt(0)").remove();
var table1 = $("#tableleague");
$.each(responseJson, function(key,value) {
var rowNew = $("<tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr>");
rowNew.children().eq(0).text(value['teams']);
rowNew.children().eq(1).text(value['playedgames']);
rowNew.children().eq(2).text(value['wongames']);
rowNew.children().eq(3).text(value['tiegames']);
rowNew.children().eq(4).text(value['lostgames']);
rowNew.children().eq(5).text(value['scoredgoal']);
rowNew.children().eq(6).text(value['receivedgoal']);
rowNew.children().eq(7).text(value['points']);
rowNew.appendTo(table1);
});
}
});
Here is how my webpage looks, with the php file response shown.
Since the response is ok, what am I doing wrong that the cells aren't filled? Thank you.

If you look at your JSON data, you can see that there are no keys such as teams or playedgames. This is because you used fetch_row() in the PHP. Change that to fetch_assoc():
while ($row = $result->fetch_assoc())
This will give you $row with the field names as keys instead of using numerical keys that fetch_row() provides.

You can turn the php json into javascript object
obj = JSON.parse(json);
es:
var json='{"ex1":"test","ex2":[{"sub1":"test"},{"sub2":""s2test}],"ex3":true}';
var obj = JSON.parse(json);
after you can acces to data with :
obj.ex1 // test
obj.ex2[0].sub2 //s2test

ajax call to php to get database rows

The following is in my file.js
function mainget(){
$.ajax({
type: 'GET',
url: 'example.php',
data:json,
success:function(data){
}
});
}
example.php
<?php
$con = mysqli_connect('address','DATBASE','pass','futureday');
$result = mysql_query("SELECT * FROM $futureday");
$array = mysql_fetch_row($result);
echo json_encode($array);
?>
I have been struck with this for the past 2 days. I have tried inserting alert as first line of function mainget , which is successful, but after that I get nothing.

You are using data property in AJAX call to indicate the json data type. It is an invalid one. Use dataType to provide the data type. data property is used to pass the datas. And also put quotes to the values like:
dataType:'json'
Also change your example.php file. There you are using mysqli_connect to connect the database, then mysql_* to execute and fetch operations. It is not correct. Use either mysqli_* or mysql_*. Edit as:
<?php
$con = mysqli_connect('address','DATBASE','pass','futureday');
$result = mysqli_query("SELECT * FROM $futureday");
$response = array();
while($array = mysqli_fetch_row($result)){
$response[]=$array;
}
echo json_encode($response);
?>

Use this
$mysqli = new mysqli('address','DATBASE','pass','futureday');
$query = "SELECT * FROM $futureday";
$results=$mysqli->query($query) ;
$res=$mysqli->fetch_array(MYSQLI_ASSOC);
echo json_encode($res);